1. Field of the Invention
The present invention relates to a vacuum processing apparatus that carries out prescribed processing on the surface of an object to be processed, in a vacuum state.
2. Description of the Prior art
Conventionally, for example, in a production process of optical discs or a production process of liquid crystal display panels, in order to execute surface processes such as spattering, etching, baking or ashing with respect to objects to be processed in a vacuum state, a vacuum processing apparatus provided with a plurality of vacuum processing chambers has been widely used (For example, Japanese Unexamined Patent Publication No. 2000-313959).
FIG. 5 and FIG. 6 show one example of a prior art vacuum processing apparatus, respectively, wherein FIG. 5 is a plan view thereof while FIG. 6 is a longitudinally sectional view thereof.
The vacuum processing apparatus 2 is provided with a vacuum transfer chamber 4, vacuum processing chambers 8 (8A through 8C) that, in a pressure-reduced state, carry out prescribed surface processing (film formation) on discs 6 (6A through 6D) being an object to be processed, and a load-lock chamber 12 that receives and transfers the discs 6 between the outside 10 and the vacuum transfer chamber 4.
The vacuum transfer chamber 4 is maintained so that the interior thereof can be maintained in a vacuum state or in a pressure-reduced state (hereinafter merely called a “pressure-reduced state”) by a first pump 14. A turbo-molecular pump (TMP), etc., may be generally used as the first pump 14, wherein high vacuum P1 of 10−4 Pa or so can be maintained in the vacuum transfer chamber 4.
The above-described vacuum processing chambers 8 (8A through 8C) are provided in a plurality (in the drawing, three chambers) so as to communicate with or be isolated from the vacuum transfer chamber 4, wherein prescribed surface processing such as spattering, etc., is carried out on the discs 6 which are objects to be processed.
The above-described load-lock chamber 12 is constructed so that the interior pressure thereof is reduced from the atmospheric pressure by a second pump 16. An oil-sealed rotary pump, etc., which can be used from the atmospheric pressure, maybe generally used as the second pump 16, wherein the interior pressure of the load-lock chamber 12 can be reduced from the atmospheric pressure to a pressure-reduced state (medium vacuum state) P2 of several Pa.
A transfer mechanism 22 for transferring the discs 6, which are the objects to be processed, is provided in the vacuum transfer chamber 4. The transfer mechanism 22 is composed of a rotating table 24 and a disc transfer carrier 26 that is able to hold and transfer the discs 6 attached to the corresponding rotating table 24 so as to advance and retreat. The disc transfer carrier 26 concurrently acts as an opening and shutting valve between the load-lock chamber 12 and the respective vacuum processing chambers 8 (8A through 8C) and the above-described vacuum transfer chamber 4.
When a disc 6 is conveyed from an outside 10 into the load-lock chamber 12, a second opening portion 12B at the outside 10 side is opened with a first opening portion 12A with the vacuum transfer chamber 4 side closed, and the disc 6 is conveyed from the outside 10 into the load-lock chamber 12. The orientation of the conveyed disc 6 is turned by a rotating mechanism (not illustrated), and the disc 6 is directly held by the disc transfer carrier 26.
Also, in the meantime, the second pump 16 still continues its rotation, and an air opening and shutting valve 20 interrupts an air line 18.
After that, the second opening portion 12B at the outside 10 side is shut, and at the same time, the air opening and shutting valve 20 is opened, wherein the interior pressure of the load-lock chamber 12 is reduced from the atmospheric pressure to a prescribed pressure-reduced state (medium vacuum state) P2. As the pressure reduction is completed, all the disc transfer carriers 26 retreat to the rotating table 24 side, and in this state, the rotating table 24 turns by 90 degrees in the horizontal direction. If the respective disc transfer carriers 26 are caused to advance after the rotating table 24 is turned, the load-lock chamber 12 and the respective vacuum processing chambers 8 are interrupted (isolated) again from the vacuum transfer chamber 4 (in a state where the held discs 6 are, respectively, moved to the adjacent chambers). After being interrupted, the air opening and shutting valve 20 is shut, the processed discs 6 (discs turned in the order from 6D to 6A) are discharged to the outside 10 by a rotating mechanism in the load-lock chamber 12. And, new unprocessed disc 6 (6A) is mounted in the disc transfer carrier 26.
As a result, the disc 6 is conveyed into the vacuum transfer chamber 4 and carried out therefrom via the load-lock chamber 12 in a state where the reduced pressure (high vacuum state) P1 in the vacuum processing chambers 8 is maintained.
In such a prior art vacuum processing apparatus 2, the interior pressure of the load-lock chamber 12 is reduced to a prescribed pressure-reduced state P2 by only the second pump 16, using a considerably long period of time (T1). At this stage, the disc transfer carrier 26 is caused to retreat, and the first opening portion 12A is opened, wherein the discs 6 are transferred.
If the first opening portion 12A is opened since the prescribed pressure-reduced state P2 is considerably higher than the pressure P1 of the vacuum transfer chamber P1, the pressure of the vacuum transfer chamber 4 and the respective vacuum processing chambers 8 connected thereto is accordingly raised.
For this reason, since there is a fear that an adverse effect due to an increase in pressure particularly after the processing in respective vacuum processing chambers 8 is given to quality, it was necessary to cause the disc transfer carrier 26 to standby in a state where the disc transfer carrier 26 is retreated to the rotating table 24 side or before commencing the processing in the processing chambers. Therefore, a long cycle time was required.
Generally, in order to secure the quality of a surface treatment of an object to be processed, in this type of vacuum processing apparatus, (1) the pressure of the vacuum processing chambers is maintained to be low in the vacuum processing chamber, (2) the remaining gas is quickly exhausted smoothly, or (3) in order to prevent the quality of the objects to be processed from being lowered immediately after the surface processing, it is necessary that the above-described pressure is devised so that the pressure is raised as little as possible in the vacuum transfer chamber. On the other hand, (4) it becomes another important object to shorten the cycle time.
In view of increasing the basic performance of the pump, a considerable effect can be recognized with respect to any one of the above objects. This is directly connected to an increase in costs. If the discharge time is set longer even in a case where the same pump is used, an effect can be recognized in the above-described points (1) through (3). However, this reverses the effect with respect to shortening of the cycle time.
In connection with point (3), prior to causing the load-lock chamber and the vacuum transfer chamber to communicate with each other, it is effective to reduce the pressure of the load-lock chamber to a pressure-reduced state close to that of the vacuum transfer chamber in advance. However, herein, a concrete problem arises.
That is, in this type of vacuum processing apparatus, the load-lock chamber is temporarily returned to the atmospheric pressure once every cycle due to its construction. At this moment, no wide-range pump has been developed, which is able to reduce the pressure from the atmospheric pressure to a pressure-reduced state at a level required for the vacuum transfer chamber by a single unit in a short time such as several seconds. Therefore, even if the pressure is reduced with a longer period of time taken, the pressure cannot be reduced to a pressure-reduced state at a level required for the vacuum transfer chamber due to shortage in the performance of a pump.
Therefore, in order to lower the pressure of the load-lock chamber to a pressure-reduced state at a level required for the vacuum transfer chamber, at present, at least two types (two units) of second pumps are required, wherein it is unavoidable to remarkably increase costs and to increase the area of occupancy.
Furthermore, if the object of making the discharge of the remaining gas smooth in point (2) is taken into consideration, the problem is further complicated.
“Remaining gas” is the general term of gases emitted from the wall surface of the vacuum processing chambers and vacuum transfer chamber, substrates of objects to be processed, and formed film layers, etc. In a narrow sense, the remaining gas means an “adverse remaining gas”, which adversely influences the quality of the surface processing, among the above. The remaining gas can be qualitatively decreased by lowering the pressure. However, the remaining gas cannot be smoothly decreased by only control of the pressure. If the remaining gas is increased, the quality of products will be resultantly worsened. Recently, this has become a serious problem as one of the issues concerning this type of apparatus.